Accepted Manuscript Title: Progress Report on New Antiepileptic Drugs: A Summary of the Twelfth Eilat Conference (EILAT XII) Author: Meir Bialer Svein I. Johannessen Ren´e H. Levy Emilio Perucca Torbj¨orn Tomson H. Steve White PII: DOI: Reference:
S0920-1211(15)00004-2 http://dx.doi.org/doi:10.1016/j.eplepsyres.2015.01.001 EPIRES 5307
To appear in:
Epilepsy Research
Received date: Accepted date:
10-12-2014 9-1-2015
Please cite this article as: Bialer, M., Johannessen, S.I., Levy, R.H., Perucca, E., Tomson, T., White, H.S.,Progress Report on New Antiepileptic Drugs: A Summary of the Twelfth Eilat Conference (EILAT XII), Epilepsy Research (2015), http://dx.doi.org/10.1016/j.eplepsyres.2015.01.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Progress Report on New Antiepileptic Drugs: A Summary of the Twelfth Eilat Conference (EILAT XII) Meir Bialera,*, Svein I. Johannessenb, René H. Levyc, Emilio Peruccad, Torbjörn
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Tomsone, H. Steve Whitef
Institute for Drug Research, School of Pharmacy and David R. Bloom Center for
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Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel
The National Center for Epilepsy, Sandvika, and Department of Pharmacology, Oslo
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University Hospital, Oslo, Norway
Departments of Pharmaceutics and Neurological Surgery, University of Washington,
Seattle, Washington, WA, USA
Division of Clinical and Experimental Pharmacology, Department of Internal
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Medicine and Therapeutics, University of Pavia, and C. Mondino National
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Neurological Institute, Pavia, Italy e
Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden
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Department of Pharmacology and Toxicology, University of Utah, Salt Lake City,
UT, USA
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*Correspondence: Prof. Meir Bialer Institute for Drug Research, School of Pharmacy and David R. Bloom Centre for
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Pharmacy, Faculty of Medicine, Ein Karem The Hebrew University of Jerusalem,
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91120 Jerusalem, Israel tel: +972-2-6758610 fax +972-2-6757246
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e-mail: [email protected]
Highlights
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The Twelfth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT XII Antiepileptic Drugs in development
Preclinical evaluation and clinical trials
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Development strategies of new AEDs
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Summary The Twelfth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT XII, took
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place in Madrid, Spain from August 31st to September 3rd, 2014. About 130 basic scientists, clinical pharmacologists and neurologists from 22 countries attended the
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conference, whose main themes included "Conquering pharmacoresistant epilepsy" ,
‘"Innovative emergency treatments", “Progress report on second-generation
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treatment” and "New methods and formulations". Consistent with previous formats of this conference, a large part of the program was devoted to a review of AEDs in
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development, as well as updates on AEDs introduced since 2004. Like the EILAT X and EILAT XI reports, the current article focuses on the preclinical and clinical
releasing
silk,
allopregnanolone
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pharmacology of AEDs that are currently in development. These include adenosine(SAGE-547),
AMP-X-0079,
brivaracetam,
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bumetanide, cannabidiol, cannabidivarin, 2-deoxy-glucose, everolimus, ganaxolone,
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huperzine A, imepitoin, minocycline, NAX 801-2, pitolisant, PRX 0023, SAGE-217,
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valnoctamide and its homologue sec-propylbutylacetamide (SPD), and VLB-01. Since the previous Eilat conference, perampanel has been introduced into the market and twelve novel potential epilepsy treatments are presented for the first time.
Keywords: Antiepileptic drugs, Drug development, Epilepsy, Pharmacology, Clinical trials, Conference
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Adenosine-Releasing Silk
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D. Boison
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Robert Stone Dow Neurobiology Labs, Legacy Research Institute, Portland, OR, USA
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Adenosine
Introduction and rationale for development
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Adenosine is an endogenous anticonvulsant responsible for seizure arrest and postictal
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refractoriness (Boison, 2007). However, maladaptive changes in adenosine
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homeostasis occur during epileptogenesis and induce a deficiency in adenosine – a characteristic pathological hallmark of human temporal lobe epilepsy (Aronica et al., 2013). In addition, reduced adenosine drives epigenetic changes thought to be instrumental in epileptogenesis (Williams-Karnesky et al., 2013). Therefore, adenosine augmentation represents a rational approach to prevent seizures and the progression of epilepsy (Boison, 2012). Systemic, largely cardiovascular, side effects of adenosine require a local mode of adenosine delivery. To deliver a defined dose of adenosine with a known release kinetics locally to the brain, a silk biopolymer was used as drug delivery system. Purified silk fibroin presents a unique option for therapeutic adenosine delivery as it is biocompatible and biodegrades slowly. Degradation kinetics can be regulated to allow control of release from weeks to years. 4 Page 4 of 166
Both silk as well as adenosine are already FDA-approved for different indications and the frequent use of silk sutures in brain confirms the feasibility of implanting silk
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biomaterials into brain.
Pharmacology
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Adenosine acts as endogenous ligand of four types of G protein coupled adenosine
receptors (A1, A2A, A2B, and A3) (Chen et al., 2013). In addition, adenosine provides
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biochemical feedback inhibition of DNA methylation (Williams-Karnesky et al.,
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2013). Adenosine homeostasis in the brain is largely under the control of metabolic clearance through adenosine kinase (ADK) expression in astrocytes (Boison, 2013).
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Anticonvulsant profile
Demonstration of the therapeutic efficacy of adenosine augmentation therapy (AAT)
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has been documented in at least 15 published research studies in two different species
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(mice and rats), and in four different models of epilepsy (mouse intrahippocampal and intraamygdaloid kainic acid (KA) model; rat hippocampal kindling model; rat
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systemic KA model) (Boison, 2012). In all four models robust seizure suppression or prevention in the absence of discernible side effects was achieved by focal AAT mediated by: (i) intraventricular implants of adenosine releasing polymeric devices; (ii) intraventricular or infrahippocampal implants of cells engineered to release
adenosine; and (iii) AAV-based gene therapy designed to reduce ADK expression in
astrocytes using antisense technology. Therapeutic efficacy has been demonstrated in a combined total of >150 different experimental epileptic animals. Dose response studies have shown that intraventricular doses of 50 to 500 ng adenosine per kg body weight per day provide effective seizure suppression in rodents, whereas doses of up to 5000 ng adenosine per kg per day were without any discernible side effects. To 5 Page 5 of 166
circumvent systemic side effects of global adenosine augmentation, a local (epileptogenic region) therapeutic approach becomes a necessity to harness the powerful anti-seizure potential of adenosine in the absence of side effects. Local AAT
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affords reliable bioavailability of adenosine within the epileptogenic brain region. AAT effectively suppressed seizures in three different models of epilepsy:
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Mouse intra-hippocampal KA model: Pharmacological augmentation of adenosine
seizures that were refractory to carbamazepine.
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signaling (ADK inhibitor or adenosine A1R agonist) completely (0/1900sz) prevented
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Mouse intra-amygdaloid KA model: Infra-hippocampal implants of adenosinereleasing mouse embryonic stem cell-derived neural precursor cells (releasing 20-40
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ng adenosine per day) completely (0/400sz) prevented the development of seizures when cells were implanted 24 h after the SE and animals were assessed for
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spontaneous seizures at 3 weeks.
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Rat kindling model: Adenosine releasing brain implants (polymers, encapsulated cells, stem cell derived implants) solidly suppressed epileptic seizures and retarded
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kindling epileptogenesis. Those studies demonstrated that the local paracrine release of adenosine resulting in adenosine concentrations 2000 ng adenosine per
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day) were well tolerated, without any gross behavioral changes of the animals. To study anti-epileptogenic properties of adenosine, we used silk-based polymers
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designed to release 1000 ng adenosine per day during a limited time span of ten days.
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When transplanted into the brain ventricle of fully kindled rats those implants completely suppressed kindled seizures only during the time span of active adenosine
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release. After expiration of adenosine release from the polymers seizures gradually resumed. When rats were kindled in the presence of adenosine releasing silk, seizure development was suppressed. Importantly, following a washout period of adenosine from the silk, kindling stimulations did not trigger any generalized seizures, indicating a novel anti-epileptogenic effect of focal adenosine delivery (Szybala et al., 2009). To further substantiate the anti-epileptogenic effect of transient adenosine release, we implanted silk-polymers releasing 250 ng adenosine / ventricle / day into the brain ventricles of epileptic rats 9 weeks after the systemic administration of KA. During active adenosine release (restricted to 10 days) the incidence of spontaneous recurrent seizures was markedly suppressed (by ~75%) in epileptic rats. Furthermore, this 7 Page 7 of 166
transient therapeutic intervention reversed the DNA hypermethylation seen in the epileptic brain, inhibited sprouting of mossy fibers in the hippocampus, and prevented the progression of epilepsy for at least 3 months. Thus, pathological changes in DNA
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methylation homeostasis may underlie epileptogenesis and reversal of these epigenetic changes with AAT may halt disease progression longterm (Williams-
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Karnesky et al., 2013).
Other pharmacological properties
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In addition to seizure suppression and prevention, adenosine augmentation has neuroprotective, antipsychotic and pro-cognitive properties (Boison, 2013; Shen et al.,
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2012).
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Anti-ictogenic mechanisms
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Mechanism(s) of action
Binding of adenosine to pre- and postsynaptic A1 receptors (Ki: 77nM; high
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expression levels in the limbic system) inhibits adenylyl cyclase activity, activates potassium channels, blocks transient calcium channels and increases intracellular calcium and inositol-1,4,5-trisphosphate levels by activating phospholipase C. Through these mechanisms A1 receptors block transmitter release and reduce the neuronal firing rate (Chen et al., 2013). Anti-epileptogenic mechanisms Adenosine is an obligatory metabolic endproduct of transmethylation reactions, which include DNA methylation. Increased adenosine shifts the S-adenosylhomocysteine (SAH) hydrolase reaction towards increased SAH production, which inhibits DNA methyltransferases through product inhibition (Williams-Karnesky et al., 2013). 8 Page 8 of 166
Transient therapeutic adenosine augmentation reduces DNA methylation status of the epileptic rodent brain and prevents disease progression long term through this
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epigenetic mechanism.
Toxicology
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Adenosine is an endogenous nucleoside that occurs in all cells of the body and is
subject to endogenous metabolic clearance mechanisms. Adenosine is FDA-approved
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for the treatment of supraventricular tachycardia and available commercially in a
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preservative-free formulation (3 mg / ml) for intravenous use. In addition, the safety of intrathecal (IT) adenosine in humans has been addressed: In a preclinical toxicity
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screening no side effects were observed in dogs with IT adenosine at 10µl/kg/h (2.4 mg/day for 48 hours, then 7.2 mg/day for 26 days). In reports using IT adenosine
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agonists for the treatment of neuropathic pain in humans, investigators demonstrated
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statistically significant reduction of neuropathic pain and allodynia by IT injection of the adenosine agonist R-PIA. No adverse effects were reported. In a Phase I clinical
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safety study 1 mg adenosine was injected IT in 12 volunteers with neuropathic pain. No adverse effects were noticed. Additional Phase I studies demonstrated the general safety of intrathecal adenosine administration in concentrations of up to 2 mg.
Pharmacokinetics and metabolic profile Intravenously administered adenosine, in concentrations used for the treatment of supraventricular tachycardia in humans, is rapidly cleared from the circulation via cellular uptake, primarily by erythrocytes and vascular endothelial cells. Intracellular adenosine is rapidly metabolized either via phosphorylation to AMP by ADK, or via deamination to inosine by adenosine deaminase (ADA) in the cytosol (Boison, 2013). 9 Page 9 of 166
Since ADK has a lower Km and Vmax than ADA, deamination plays a significant role only when cytosolic adenosine saturates the phosphorylation pathway. Inosine formed by deamination of adenosine can leave the cell intact or can be degraded to
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hypoxanthine, xanthine, and finally uric acid. AMP formed by phosphorylation of adenosine is incorporated into the high-energy phosphate pool. In the brain, adenosine
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clearance is largely mediated by ADK activity (Boison, 2013). Extracellular adenosine is primarily cleared by cellular uptake with a half-life of less than 10
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seconds in whole blood and less than 10 minutes in brain. Excessive amounts of
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adenosine can be deaminated by adenosine ecto-deaminase (ectoADA). Adenosine requires no hepatic or renal function for its activation or inactivation, and hepatic and
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renal failure would not be expected to alter its effectiveness or tolerability.
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Drug interactions
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The methylxanthines theophylline and caffeine competitively antagonize adenosine's
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effects on adenosine receptors. Dipyridamole potentiates the action of adenosine.
Efficacy data
Efficacy data of adenosine releasing silk are available from rodent models of epilepsy as described above. It is estimated that the minimally effective dose of adenosine delivered by a local brain implant is in the range of 50 to 500 ng adenosine per kg per day.
Tolerability and adverse effect profile Adverse effects of intravenous adenosine (6 mg given as a rapid intravenous bolus administered over a 1 to 2 second period) in adult subjects for the treatment of 10 Page 10 of 166
supraventricular tachycardia have been found to affect a variety of systems. Cardiovascular effects included facial flushing (18%), headache (2%), sweating, palpitations, chest pain, hypotension (less than 1%). Respiratory effects included
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shortness of breath/dyspnea (12%), chest pressure (7%), hyperventilation, head pressure (less than 1%). Central Nervous System (CNS) effects included
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lightheadedness (2%), dizziness, tingling in arms, numbness (1%), apprehension,
blurred vision, burning sensation, heaviness in arms, neck and back pain (less than
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1%). Gastrointestinal effects were nausea (3%), metallic taste, tightness in throat,
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pressure in groin (less than 1%). The local application of adenosine in the brain is
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expected to avoid any of the above-mentioned systemic non-CNS side effects.
Planned studies
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Further preclinical studies for the application “anti-epileptogenesis” are planned. This
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includes determination of minimally effective anti-epileptogenic doses of adenosine, optimization of the delivery procedure, further mechanistic studies and long-term
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efficacy studies in rodent models of epileptogenesis.
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Allopregnanolone (SAGE-547) Injection S.J. Kanes, J. Doherty, R. Hammond, M. Rogawski, A. Robichaud, J. Jonas.
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Allopregnanolone (SAGE-547)
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Sage Therapeutics, Cambridge, MA 02142, USA
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Introduction and rationale for development
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SAGE-547 (allopregnanolone) Injection is a solution of 5 mg/mL allopregnanolone
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and 250 mg/mL betadex sulfobutyl ether sodium, NF (Captisol®). Allopregnanolone Injection (SAGE-547) is being developed for the treatment of super-refractory SE (SRSE).
Allopregnanolone is an endogenously occurring neuroactive steroid and a principal metabolite of progesterone formed in the corpus luteum of the ovary, adrenal cortex and CNS (Paul & Purdy, 1992). Endogenous concentrations of allopregnanolone are at their highest in women during the third trimester of pregnancy, and approximate 157 nM at time of parturition (Luisi et al, 2000). Allopregnanolone is a potent positive allosteric modulator of GABAA receptor responses (Lambert et al,
2003). Through GABAA receptor modulation,
allopregnanolone possesses potent anxiolytic, sedative and anticonvulsant activity 12 Page 12 of 166
when studied in non-clinical in vitro and in vivo model systems (Belelli et al, 1989; Bitran et al, 1991; Wieland et al, 1991).
Anticonvulsant profile (animal models/electrophysiology)
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Pharmacology
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There is ample evidence indicating a role for allopregnanolone in the treatment of seizures and status epilepticus (SE). Allopregnanolone has anticonvulsant properties
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in a variety of acute seizure models, including the pentylenetetrazol (PTZ), 6Hz, The acute anticonvulsant efficacy of
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bicuculline, and picrotoxin models.
allopregnanolone in the PTZ-induced seizure model in mice is maintained upon repeat
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dosing. Allopregnanolone produces complete suppression of generalized amygdalakindled convulsions and protection against pilocarpine- or kainate-induced limbic
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seizures and SE, with higher protective index values than clonazepam. In the rat
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kainate-induced model of SE, allopregnanolone (30 mg/kg, ip) eliminated SE whether administered at either 10 minutes or at 70 minutes following kainate administration,
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whereas diazepam (5 mg/kg, ip) was only effective at 10 minutes following kainate administration.
These results support the hypothesis that enhancement of extra-
synaptic GABAA receptor function by allopregnanolone may provide anticonvulsant
efficacy when prolonged seizure activity has become pharmaco-resistant to benzodiazepine treatment.
Mechanism(s) of action Mammalian GABAA receptors are heteropentameric chloride-conducting ion channels that mediate fast inhibition of synaptic transmission via a reduction of neuronal membrane excitability. These ionotropic receptors are called GABAA receptors to 13 Page 13 of 166
distinguish them from metabotropic GABA receptor (G-protein coupled) (GABAB) receptors that mediate a slower form of synaptic inhibition. Allosteric potentiation of GABAA receptor function by allopregnanolone has been
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extensively documented (Belelli, 2002; Belelli et al, 2005). Consistent with this literature, SAGE-547 potentiated GABA-mediated currents from recombinant human
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GABAA receptors expressed in heterologous mammalian cell lines. SAGE-547 produced a potent, concentration-dependent enhancement of GABA-evoked currents
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recorded using whole-cell patch electrophysiology from Ltk-1 cells expressing α1β2γ2
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receptors, with a half maximal effective concentration (EC50) of 60 nM and a maximal potentiation of 380% for agonist (EC20)-induced currents. SAGE-547 also produced a
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potent enhancement of α4β3δ receptors, with an EC50 of 80 nM and a maximal potentiation of 418% for agonist (EC20)-induced currents.
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In addition to allosteric enhancement of channel function, allopregnanolone
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modulates the binding of a variety of other ligands to the GABAA receptor, including the picrotoxin/convulsant site labeled by [35S]-t-butylbicyclophosphorothionate
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(TBPS) (Concas et al, 1996). Consistent with this literature, SAGE-547 potently inhibited [35S]-TBPS binding, displacing the radioligand from rat cerebral cortex membranes with an inhibition constant (Ki) of 18 nM.
Toxicology
The minimum lethal doses for allopregnanolone in mice, rats, and rabbits are 20, 15, and 7 mg/kg intravenously, respectively. Based on the correction for body surface area across the species, these are equivalent to human doses of 1.6, 2.4, and 2.25 mg/kg intravenously, or 112, 168, and 158 mg in a 70 kg human (Gyermek et al, 1968). 14 Page 14 of 166
A recently published abstract presented the determination of maximum tolerated doses (MTD) of allopregnanolone in neonatal beagle dogs after bolus and i.v. infusions (Steinmetz et al, 2013). One pup administered allopregnanolone via i.v.
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bolus (50 mg/kg), was not responsive to stimuli and exhibited, shallow rapid breathing but fully recovered without intervention. One pup administered 20 mg/kg
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allopregnanolone over a 4 hr i.v. infusion, fell asleep approximately 30 min post dose
and recovered without intervention. No allopregnanolone-related adverse effects on
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chemistry or hematology labs were observed. Of note, studies with allopregnanolone
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by the same investigators suggested that the presence of isoflurane anesthesia resulted in an MTD of 2-fold in one of the three donors. Although SAGE-547 shows the potential to induce CYP2B6, the increase was small
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at the highest concentration tested. Clinical exposures are targeted at 150 nM, which are well below the 30-50 μM required for induction of the enzyme. The potential for SAGE-547 (1 and 10 µM) to inhibit human CYP1A2, CYP2C9, CYP 2C19, CYP2D6, and CYP3A4 was investigated in vitro utilizing human liver
microsomes incubated in the presence of clinically relevant marker substrates. No inhibition was observed at 1 µM of SAGE-547. At 10 µM, no inhibition was observed for any of the CYPs, except for CYP2C9, which showed 47% inhibition. This result was followed up by determining half maximal inhibitory concentration (IC50) and Ki for CYP2C9 utilizing human liver microsomes and measuring formation of 4’hydroxy-diclofenac from diclofenac. IC50 was 0.41 µM and Ki was 0.256 µM. There 16 Page 16 of 166
was no evidence of time-dependent or metabolism-dependent inhibition based on monitoring IC50-shift after pre-incubation. SAGE-547 has the potential to alter the
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metabolism of CYP2C9 substrates when administered concomitantly.
Tolerability and adverse effect profile
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With systemic exposures up to 150 nM, no drug-related serious TEAEs have been reported. Drug related TEAEs reported with i.v. allopregnanolone are generally mild,
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the most frequently reported (>5% patients) being feelings of intoxication, sedation,
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and vertigo. One patient experienced an anxiety attack, which is potentially a withdrawal effect. Clinical observations in the i.v. studies included decreased saccadic
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eye movements, reduced episodic memory, as well as reduced plasma levels of LH and FSH. (Timby et al, 2006; Timby et al, 2011; van Broekhoven et al, 2007; Kask et
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al, 2008; Kask et al, 2009).
Efficacy data and ongoing study
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An open-label Phase I/II clinical trial was initiated to study the safety, tolerability and
efficacy of SAGE-547 in at least 10 adult patients with SRSE. This trial is enrolling patients who have been in SE for at least 24 h despite treatment with first and second line SE treatments and have either failed to have SE controlled after 24 hours on a third-line general anesthetic (GA) agent or if SE was controlled by a GA have failed at least 1 wean attempt. A patient is excluded from the trial if pregnant or lactating, or if the patient has a known allergy to progesterone or allopregnanolone, has clinically significant ECG abnormalities, has a significant medical or surgical condition that may compromise vital organ systems, has been exposed to another experimental treatment within 30 days, is receiving a continuous 17 Page 17 of 166
i.v. AED (third-line agent) for seizure suppression or burst-suppression that will require greater than 24 h to wean, has enrolled in this trial previously, or if the SRSE was due to anoxic/hypoxic encephalopathy.
The figure below demonstrates the
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design of the screening and treatment periods of this trial. Following the treatment period, there will be an acute two day follow-up period and an extended three-week
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follow-up period.
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Figure 1: Trial design of SABE-547 in Super-refractory status epilepticus (SRSE)
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The primary objective of this trial are to evaluate the safety and tolerability of SAGE-
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547 injection in SRSE patients as assessed by monitoring treatment-emergent adverse
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events (TEAE), EEG, physical and neurological examinations, vital signs, clinical laboratory measures, ECGs and concomitant medication usage.
The secondary
objective of this trial is to assess the efficacy of SAGE-547 in SRSE, a assessed by the need to place the patient back into general anesthesia for seizure control during administration of SAGE-547 prior to taper.
Other secondary objectives include
duration of response, as well as changes in behavior as measured by rating scales of agitation, depth of coma, and survival. This trial is ongoing. To date, 4 patients have completed the full 5 day administration of SAGE-547 at a target plasma exposure of 150 nM and 30-day follow-up period. All have met the key efficacy endpoint of SE control during SAGE-547 administration. To date there have been no drug-related
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serious TEAEs in these patients.
Planned studies
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larger scale controlled trial in a similar population of SRSE patients.
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Depending upon the outcome of the Phase I/II trial, the plan is to follow-up with a
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AMP-X-0079 A. Pesyan1, R. J Porter2 AurimMed Pharma, Park City, Utah, USA1
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University of Pennsylvania, Philadelphia, PA, and USUHS, Bethesda MD, USA2
Introduction and rationale for development
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AurimMed Pharma, Inc. is developing innovative prescription drugs using the Privileged Structure Platform™ (PSP) strategy to generate lead compounds. The PSP
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approach ensures that the process of drug design proceeds exclusively from a highly enriched pool of pharmaceutically and medicinally relevant chemical structures,
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greatly shortening product development times while enhancing clinical success (Muller, 2003; DeSimone et al., 2004; Costantino and Barlocco, 2006; Duarte et al.,
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2007). The PSP strategy has been used in the development of novel anti-seizure drug
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candidates with potential superior efficacy and greatly diminished adverse effects.
Pharmacology
Anticonvulsant profile (animal models/electrophysiology) Based on studies in animal models, AurimMed Pharma’s most advanced AED candidate, AMP-X-0079, has a very broad spectrum, with the potential to become a superb anti-seizure drug for a variety of seizure types, including absence/petit mal, tonic-clonic and myoclonic seizures as well as status epilepticus. In addition to the
compound’s broad spectrum of activities across a number of animal models (Tables 1 and 2), it has (in rodent models) good oral bioavailability, CNS penetration, long duration of action, good neurological safety margins (Protective Indices, PIs), and substantial potency. 20 Page 20 of 166
AMP-X-0079 anticonvulsant data included in Tables 1 and 2 were largely derived from the Anticonvulsant Screening Program of NINDS, NIH. As one can see, AMPX-0079 is active in all the models tested, including the new semi-chronic mesial
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temporal lobe epilepsy model. Protective Index (PI) = TD50/ED50. (“Toxicity” is defined here as rotarod motor impairment in mice and a battery of tests to determine
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neurological deficit as indicated by ataxia or other minimal motor impairment (MMI) in rats.)
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In studies conducted by the NIH and the US Department of Defense (DOD), AMP-X-
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0079 is active in models of chemically induced status epilepticus (SE), both when administered at the time of the chemical insult (time zero) as well as 30 minutes after
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the appearance of seizures; the compound is therefore effective in both the prevention and the treatment of SE. Moreover, in a pilocarpine-induced model of SE, followed
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by extensive, 9 day, evaluation in a Morris water maze task, AMP-X-0079 preserved
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cognition, spatial learning and memory. The compound also demonstrated substantial in vivo neuroprotective effects in the dentate gyrus, CA1, and CA3 hippocampal
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neurons in the brains of a vast majority (87%) of the treated animals (results confirmed histologically). In the pilocarpine insult and SE, 100% of the AMP-X0079-treated animals survived compared to 54% of controls. In addition, the compound is active against non-convulsive seizures in benzodiazepine-resistant electrographic status epilepticus (ESE), confirmed by EEG studies (Lehmkuhle et al.,
2009).
AMP-X-0079 has been shown in in vivo studies to be orally bioavailable, fast-acting (rapid oral absorption within 15 minutes), with a reasonably long pharmacological half-life in animal models. The compound passes the blood-brain barrier, thereby manifesting its pharmacological effects directly in the central nervous system. 21 Page 21 of 166
Because of its unique pharmacological profile and significant suppression of ESE, the lead candidate (AMP-X-0079) was tested against a nerve agent (i.e., soman) by the U.S. Army Medical Research Institute of Chemical Defense (USAMRICD) of the
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DOD. AMP-X-0079 is one of the few drugs capable of terminating ongoing status epilepticus seizures due to this nerve agent. It controls seizure very rapidly (typically
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50%, with a half-life from 2-8 h after oral administration. In vitro metabolic profiling was conducted in cryopreserved human, mouse, rat, and dog hepatocytes, and reveals essentially four discreet metabolites. Although structural identification of these metabolites has not been conducted to date,
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their molecular mass suggests that they all result from single hydroxylations. In addition, there is no evidence for the occurrence of unique human metabolites.
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Drug interactions Although no formal drug interaction studies have been conducted, in vitro CYP
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inhibition (IC50) is >30 µM for all major isozymes, suggesting low potential for SAGE-217 to inhibit the metabolism of substrates for those enzymes. Induction of
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drug metabolizing enzymes assessed in human hepatocytes indicates low level of
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induction of CYP3A4 and CYP2B6, suggesting that SAGE-217 has the potential to
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alter the pharmacokinetics of substrates for those enzymes.
Efficacy data
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Tolerability and side effect profile
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To date, no human studies have been completed with SAGE-217.
Planned studies
Currently, , to support a first in man (FIM) study, a number of IND-enabling toxicology studies are planned or on-going, including 28-day general toxicology studies in rats and dogs, a genetic toxicity battery of Ames, rat micronucleus and Comet assays, and a safety pharmacology battery of rat CNS, rat respiratory and dog telemetry studies. In addition, to support later stage clinical investigations and a potential market launch, Sage Therapeutics will perform sub-chronic (3-month) and chronic (6 or 9-month) studies in rats and dogs, reproductive toxicology studies with 110 Page 110 of 166
Seg II in rats and rabbit. Rat Seg I and Seg III, a battery of abuse liability of drug dependence, drug discrimination and self administration, and carcinogenicity studies in rats and mice are also planned. Pending outcome of these trials, a Phase III clinical
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Valnoctamide and sec-Butylpropylacetamide (SPD): Second Generation Drugs to Valproic Acid (VPA)
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M. Bialer,1 S. Kadosh2 and B.Yagen1 Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew
StatExcellence, Kfar Saba, Israel
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University of Jerusalem, Israel
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* CHCONH2 CH2
* CHCONH2 CH2
CH3
sec-Butyl-propylacetamide (SPD)
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Valnoctamide (VCD)
CH2
CH
*
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CH3
CH3
Introduction and rationale for development Valnoctamide (VCD) is a CNS-active chiral constitutional isomer of valpromide, the corresponding amide of valproic acid (VPA). Since EILAT XI (2012), VCD underwent phase IIb clinical trial in patients with acute mania. VCD's one-carbon homologue sec-butyl-propylacetamide (SPD) was evaluated in a wide array of anticonvulsant models (White et al., 2012; Pouliot et al., 2013; Shekh-Ahmad et al., 2013). Both VCD and SPD possess two stereogenic centers in their chemical structure (denoted above with the asterisk *) and exhibit stereoselective pharmacokinetics (PK) in humans (VCD) and animals (Bialer and Yagen, 2007; Bialer, 2012). Consequently, the pharmacodynamics (PD; anticonvulsant activity) and PK of the four individual 112 Page 112 of 166
stereoisomers of VCD and SPD were evaluated in several rodent anticonvulsant models including: maximal electroshock (MES), 6Hz psychomotor, subcutaneous metrazol (scMet) and the pilocarpine- and soman-induced status epilepticus (SE) (Hen
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et al., 2013; Shekh-Ahmad, 2014). The PK-PD (anticonvulsant activity) relationship of VCD and SPD stereoisomers were evaluated following i.p. administration (70 or 60
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mg/kg) to rats. Induction of neural tube defects (NTDs) by VCD and SPD stereoisomers was evaluated in a mouse strain highly-susceptible to teratogen-induced
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us
NTD.
Pharmacology
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Anticonvulsant profile (animal models/electrophysiology) Valnoctamide (VCD)
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VCD (racemate and/or its individual enantiomers) demonstrated anticonvulsant
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activity in a wide array of anticonvulsant models in mice and rats (MES, scMet and 6Hz, kindling) as described in the previous Eilat (EILAT X & XI) Conference
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manuscripts (Bialer et al., 2010 & 2013). In mice VCD four individual stereoisomers exhibited similar anticonvulsant activity
to one another as well as to racemic-VCD in the scMet and 6Hz tests, while at the MES test (2R,3R)-VCD was more potent than its enantiomer (2S,3S)-VCD and diastereoisomer (2S,3R)-VCD. In rats (p.o.) racemic-VCD and its four individual stereoisomers exhibited similar anticonvulsant activity in the MES test while (2R,3S)-VCD was the most potent compound at the scMet test with an ED50 value 5-
times more potent than the racemate (Shekh-Ahmad et al, 2014). Racemic-VCD as well as (2R,3S)-VCD and (2S,3S)-VCD administered at seizure onset blocked the pilocarpine-induced SE with similar ED50 values of about 40 113 Page 113 of 166
mg/kg. However, racemic-VCD and its individual strereoisomers lost this anti-SE activity when given (75-100 mg/kg) 30 min after seizure onset (Shekh-Ahmad et al., 2014).
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Racemic-VCD administered with the standard medical countermeasures at treatment delays of 5 min, 20 min and 40 min after seizure onset was capable of stopping
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soman-induced SE seizures with ED50 values of 26mg/kg, 60mg/kg and 62mg/kg, respectively. Following administration of VCD the average latency (sec) for
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electrographic seizure termination (mean±SEM) at 5 min, 20 min and 40 min was:
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115±15, 497±15 and 1,336±318, respectively . VCD is one of the few drugs effective
sec-Butylpropylacetamide (SPD)
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at 40 min delay at the soman-induced SE model (Shekh-Ahmad et al., 2014).
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Racemic-SPD had a wide spectrum of anticonvulsant activity similar to VPA but was
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4-30 times more potent than VPA in a wide array of anticonvulsant animal models (Shekh-Ahmad et al., 2013). Three SPD individual stereoisomers: (2R,3R)-SPD,
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(2S,3S)-SPD and (2R,3S)-SPD, exhibited anticonvulsant activity similar to racemicSPD, while (2S,3R)-SPD exhibited less potent anticonvulsant activity at the rat (po) MES model (Hen et al., 2013).
SPD stereoisomers, administered 30 min after the first observed Stage 3 motor seizure at the lithium-pilocarpine induced SE model, prevented the expression of further convulsive seizures in a dose-dependent fashion with ED50 values ranging
between 95-135 mg/kg. (2R,3R)-SPD was the least potent SPD stereoisomer (ED50 >130 mg/kg) (Hen et al., 2013). SPD and its individual stereoisomers were capable of stopping soman-induced SE seizures with ED50 values ranging between 40 to 71 mg/kg. Following administration 114 Page 114 of 166
of SPD individual stereoisomers the average latency (sec) for electrographic seizure termination at the 20-min treatment delay time (mean±SEM) was: 550±149; n=16 [(2R,3R)-SPD], 994±280; n=8 [(2R,3S)-SPD], 719±216; n=15 [(2S,3R)-SPD],
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1589±684; n=13 [(2S,3S)-SPD] . All four individual SPD stereoisomers had a steep dose response curve with Hill (shape) coefficient of 4.5-8.9 that lead to a tight 95%
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confidence interval around their ED50 values. (2R,3R)-SPD was more potent than racemic-SPD as well as SPD three other individual stereoisomers (p
S0920-1211(15)00004-2 http://dx.doi.org/doi:10.1016/j.eplepsyres.2015.01.001 EPIRES 5307
To appear in:
Epilepsy Research
Received date: Accepted date:
10-12-2014 9-1-2015
Please cite this article as: Bialer, M., Johannessen, S.I., Levy, R.H., Perucca, E., Tomson, T., White, H.S.,Progress Report on New Antiepileptic Drugs: A Summary of the Twelfth Eilat Conference (EILAT XII), Epilepsy Research (2015), http://dx.doi.org/10.1016/j.eplepsyres.2015.01.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Progress Report on New Antiepileptic Drugs: A Summary of the Twelfth Eilat Conference (EILAT XII) Meir Bialera,*, Svein I. Johannessenb, René H. Levyc, Emilio Peruccad, Torbjörn
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Tomsone, H. Steve Whitef
Institute for Drug Research, School of Pharmacy and David R. Bloom Center for
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Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem, Israel
The National Center for Epilepsy, Sandvika, and Department of Pharmacology, Oslo
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b
University Hospital, Oslo, Norway
Departments of Pharmaceutics and Neurological Surgery, University of Washington,
Seattle, Washington, WA, USA
Division of Clinical and Experimental Pharmacology, Department of Internal
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Medicine and Therapeutics, University of Pavia, and C. Mondino National
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Neurological Institute, Pavia, Italy e
Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden
f
Department of Pharmacology and Toxicology, University of Utah, Salt Lake City,
UT, USA
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*Correspondence: Prof. Meir Bialer Institute for Drug Research, School of Pharmacy and David R. Bloom Centre for
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Pharmacy, Faculty of Medicine, Ein Karem The Hebrew University of Jerusalem,
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91120 Jerusalem, Israel tel: +972-2-6758610 fax +972-2-6757246
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e-mail: [email protected]
Highlights
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The Twelfth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT XII Antiepileptic Drugs in development
Preclinical evaluation and clinical trials
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Development strategies of new AEDs
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Summary The Twelfth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT XII, took
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place in Madrid, Spain from August 31st to September 3rd, 2014. About 130 basic scientists, clinical pharmacologists and neurologists from 22 countries attended the
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conference, whose main themes included "Conquering pharmacoresistant epilepsy" ,
‘"Innovative emergency treatments", “Progress report on second-generation
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treatment” and "New methods and formulations". Consistent with previous formats of this conference, a large part of the program was devoted to a review of AEDs in
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development, as well as updates on AEDs introduced since 2004. Like the EILAT X and EILAT XI reports, the current article focuses on the preclinical and clinical
releasing
silk,
allopregnanolone
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pharmacology of AEDs that are currently in development. These include adenosine(SAGE-547),
AMP-X-0079,
brivaracetam,
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bumetanide, cannabidiol, cannabidivarin, 2-deoxy-glucose, everolimus, ganaxolone,
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huperzine A, imepitoin, minocycline, NAX 801-2, pitolisant, PRX 0023, SAGE-217,
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valnoctamide and its homologue sec-propylbutylacetamide (SPD), and VLB-01. Since the previous Eilat conference, perampanel has been introduced into the market and twelve novel potential epilepsy treatments are presented for the first time.
Keywords: Antiepileptic drugs, Drug development, Epilepsy, Pharmacology, Clinical trials, Conference
3 Page 3 of 166
Adenosine-Releasing Silk
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D. Boison
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Robert Stone Dow Neurobiology Labs, Legacy Research Institute, Portland, OR, USA
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Adenosine
Introduction and rationale for development
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Adenosine is an endogenous anticonvulsant responsible for seizure arrest and postictal
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refractoriness (Boison, 2007). However, maladaptive changes in adenosine
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homeostasis occur during epileptogenesis and induce a deficiency in adenosine – a characteristic pathological hallmark of human temporal lobe epilepsy (Aronica et al., 2013). In addition, reduced adenosine drives epigenetic changes thought to be instrumental in epileptogenesis (Williams-Karnesky et al., 2013). Therefore, adenosine augmentation represents a rational approach to prevent seizures and the progression of epilepsy (Boison, 2012). Systemic, largely cardiovascular, side effects of adenosine require a local mode of adenosine delivery. To deliver a defined dose of adenosine with a known release kinetics locally to the brain, a silk biopolymer was used as drug delivery system. Purified silk fibroin presents a unique option for therapeutic adenosine delivery as it is biocompatible and biodegrades slowly. Degradation kinetics can be regulated to allow control of release from weeks to years. 4 Page 4 of 166
Both silk as well as adenosine are already FDA-approved for different indications and the frequent use of silk sutures in brain confirms the feasibility of implanting silk
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biomaterials into brain.
Pharmacology
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Adenosine acts as endogenous ligand of four types of G protein coupled adenosine
receptors (A1, A2A, A2B, and A3) (Chen et al., 2013). In addition, adenosine provides
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biochemical feedback inhibition of DNA methylation (Williams-Karnesky et al.,
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2013). Adenosine homeostasis in the brain is largely under the control of metabolic clearance through adenosine kinase (ADK) expression in astrocytes (Boison, 2013).
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Anticonvulsant profile
Demonstration of the therapeutic efficacy of adenosine augmentation therapy (AAT)
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has been documented in at least 15 published research studies in two different species
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(mice and rats), and in four different models of epilepsy (mouse intrahippocampal and intraamygdaloid kainic acid (KA) model; rat hippocampal kindling model; rat
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systemic KA model) (Boison, 2012). In all four models robust seizure suppression or prevention in the absence of discernible side effects was achieved by focal AAT mediated by: (i) intraventricular implants of adenosine releasing polymeric devices; (ii) intraventricular or infrahippocampal implants of cells engineered to release
adenosine; and (iii) AAV-based gene therapy designed to reduce ADK expression in
astrocytes using antisense technology. Therapeutic efficacy has been demonstrated in a combined total of >150 different experimental epileptic animals. Dose response studies have shown that intraventricular doses of 50 to 500 ng adenosine per kg body weight per day provide effective seizure suppression in rodents, whereas doses of up to 5000 ng adenosine per kg per day were without any discernible side effects. To 5 Page 5 of 166
circumvent systemic side effects of global adenosine augmentation, a local (epileptogenic region) therapeutic approach becomes a necessity to harness the powerful anti-seizure potential of adenosine in the absence of side effects. Local AAT
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affords reliable bioavailability of adenosine within the epileptogenic brain region. AAT effectively suppressed seizures in three different models of epilepsy:
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Mouse intra-hippocampal KA model: Pharmacological augmentation of adenosine
seizures that were refractory to carbamazepine.
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signaling (ADK inhibitor or adenosine A1R agonist) completely (0/1900sz) prevented
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Mouse intra-amygdaloid KA model: Infra-hippocampal implants of adenosinereleasing mouse embryonic stem cell-derived neural precursor cells (releasing 20-40
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ng adenosine per day) completely (0/400sz) prevented the development of seizures when cells were implanted 24 h after the SE and animals were assessed for
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spontaneous seizures at 3 weeks.
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Rat kindling model: Adenosine releasing brain implants (polymers, encapsulated cells, stem cell derived implants) solidly suppressed epileptic seizures and retarded
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kindling epileptogenesis. Those studies demonstrated that the local paracrine release of adenosine resulting in adenosine concentrations 2000 ng adenosine per
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day) were well tolerated, without any gross behavioral changes of the animals. To study anti-epileptogenic properties of adenosine, we used silk-based polymers
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designed to release 1000 ng adenosine per day during a limited time span of ten days.
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When transplanted into the brain ventricle of fully kindled rats those implants completely suppressed kindled seizures only during the time span of active adenosine
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release. After expiration of adenosine release from the polymers seizures gradually resumed. When rats were kindled in the presence of adenosine releasing silk, seizure development was suppressed. Importantly, following a washout period of adenosine from the silk, kindling stimulations did not trigger any generalized seizures, indicating a novel anti-epileptogenic effect of focal adenosine delivery (Szybala et al., 2009). To further substantiate the anti-epileptogenic effect of transient adenosine release, we implanted silk-polymers releasing 250 ng adenosine / ventricle / day into the brain ventricles of epileptic rats 9 weeks after the systemic administration of KA. During active adenosine release (restricted to 10 days) the incidence of spontaneous recurrent seizures was markedly suppressed (by ~75%) in epileptic rats. Furthermore, this 7 Page 7 of 166
transient therapeutic intervention reversed the DNA hypermethylation seen in the epileptic brain, inhibited sprouting of mossy fibers in the hippocampus, and prevented the progression of epilepsy for at least 3 months. Thus, pathological changes in DNA
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methylation homeostasis may underlie epileptogenesis and reversal of these epigenetic changes with AAT may halt disease progression longterm (Williams-
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Karnesky et al., 2013).
Other pharmacological properties
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In addition to seizure suppression and prevention, adenosine augmentation has neuroprotective, antipsychotic and pro-cognitive properties (Boison, 2013; Shen et al.,
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2012).
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Anti-ictogenic mechanisms
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Mechanism(s) of action
Binding of adenosine to pre- and postsynaptic A1 receptors (Ki: 77nM; high
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expression levels in the limbic system) inhibits adenylyl cyclase activity, activates potassium channels, blocks transient calcium channels and increases intracellular calcium and inositol-1,4,5-trisphosphate levels by activating phospholipase C. Through these mechanisms A1 receptors block transmitter release and reduce the neuronal firing rate (Chen et al., 2013). Anti-epileptogenic mechanisms Adenosine is an obligatory metabolic endproduct of transmethylation reactions, which include DNA methylation. Increased adenosine shifts the S-adenosylhomocysteine (SAH) hydrolase reaction towards increased SAH production, which inhibits DNA methyltransferases through product inhibition (Williams-Karnesky et al., 2013). 8 Page 8 of 166
Transient therapeutic adenosine augmentation reduces DNA methylation status of the epileptic rodent brain and prevents disease progression long term through this
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epigenetic mechanism.
Toxicology
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Adenosine is an endogenous nucleoside that occurs in all cells of the body and is
subject to endogenous metabolic clearance mechanisms. Adenosine is FDA-approved
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for the treatment of supraventricular tachycardia and available commercially in a
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preservative-free formulation (3 mg / ml) for intravenous use. In addition, the safety of intrathecal (IT) adenosine in humans has been addressed: In a preclinical toxicity
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screening no side effects were observed in dogs with IT adenosine at 10µl/kg/h (2.4 mg/day for 48 hours, then 7.2 mg/day for 26 days). In reports using IT adenosine
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agonists for the treatment of neuropathic pain in humans, investigators demonstrated
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statistically significant reduction of neuropathic pain and allodynia by IT injection of the adenosine agonist R-PIA. No adverse effects were reported. In a Phase I clinical
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safety study 1 mg adenosine was injected IT in 12 volunteers with neuropathic pain. No adverse effects were noticed. Additional Phase I studies demonstrated the general safety of intrathecal adenosine administration in concentrations of up to 2 mg.
Pharmacokinetics and metabolic profile Intravenously administered adenosine, in concentrations used for the treatment of supraventricular tachycardia in humans, is rapidly cleared from the circulation via cellular uptake, primarily by erythrocytes and vascular endothelial cells. Intracellular adenosine is rapidly metabolized either via phosphorylation to AMP by ADK, or via deamination to inosine by adenosine deaminase (ADA) in the cytosol (Boison, 2013). 9 Page 9 of 166
Since ADK has a lower Km and Vmax than ADA, deamination plays a significant role only when cytosolic adenosine saturates the phosphorylation pathway. Inosine formed by deamination of adenosine can leave the cell intact or can be degraded to
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hypoxanthine, xanthine, and finally uric acid. AMP formed by phosphorylation of adenosine is incorporated into the high-energy phosphate pool. In the brain, adenosine
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clearance is largely mediated by ADK activity (Boison, 2013). Extracellular adenosine is primarily cleared by cellular uptake with a half-life of less than 10
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seconds in whole blood and less than 10 minutes in brain. Excessive amounts of
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adenosine can be deaminated by adenosine ecto-deaminase (ectoADA). Adenosine requires no hepatic or renal function for its activation or inactivation, and hepatic and
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renal failure would not be expected to alter its effectiveness or tolerability.
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Drug interactions
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The methylxanthines theophylline and caffeine competitively antagonize adenosine's
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effects on adenosine receptors. Dipyridamole potentiates the action of adenosine.
Efficacy data
Efficacy data of adenosine releasing silk are available from rodent models of epilepsy as described above. It is estimated that the minimally effective dose of adenosine delivered by a local brain implant is in the range of 50 to 500 ng adenosine per kg per day.
Tolerability and adverse effect profile Adverse effects of intravenous adenosine (6 mg given as a rapid intravenous bolus administered over a 1 to 2 second period) in adult subjects for the treatment of 10 Page 10 of 166
supraventricular tachycardia have been found to affect a variety of systems. Cardiovascular effects included facial flushing (18%), headache (2%), sweating, palpitations, chest pain, hypotension (less than 1%). Respiratory effects included
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shortness of breath/dyspnea (12%), chest pressure (7%), hyperventilation, head pressure (less than 1%). Central Nervous System (CNS) effects included
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lightheadedness (2%), dizziness, tingling in arms, numbness (1%), apprehension,
blurred vision, burning sensation, heaviness in arms, neck and back pain (less than
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1%). Gastrointestinal effects were nausea (3%), metallic taste, tightness in throat,
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pressure in groin (less than 1%). The local application of adenosine in the brain is
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expected to avoid any of the above-mentioned systemic non-CNS side effects.
Planned studies
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Further preclinical studies for the application “anti-epileptogenesis” are planned. This
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includes determination of minimally effective anti-epileptogenic doses of adenosine, optimization of the delivery procedure, further mechanistic studies and long-term
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efficacy studies in rodent models of epileptogenesis.
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Allopregnanolone (SAGE-547) Injection S.J. Kanes, J. Doherty, R. Hammond, M. Rogawski, A. Robichaud, J. Jonas.
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Allopregnanolone (SAGE-547)
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Sage Therapeutics, Cambridge, MA 02142, USA
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Introduction and rationale for development
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SAGE-547 (allopregnanolone) Injection is a solution of 5 mg/mL allopregnanolone
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and 250 mg/mL betadex sulfobutyl ether sodium, NF (Captisol®). Allopregnanolone Injection (SAGE-547) is being developed for the treatment of super-refractory SE (SRSE).
Allopregnanolone is an endogenously occurring neuroactive steroid and a principal metabolite of progesterone formed in the corpus luteum of the ovary, adrenal cortex and CNS (Paul & Purdy, 1992). Endogenous concentrations of allopregnanolone are at their highest in women during the third trimester of pregnancy, and approximate 157 nM at time of parturition (Luisi et al, 2000). Allopregnanolone is a potent positive allosteric modulator of GABAA receptor responses (Lambert et al,
2003). Through GABAA receptor modulation,
allopregnanolone possesses potent anxiolytic, sedative and anticonvulsant activity 12 Page 12 of 166
when studied in non-clinical in vitro and in vivo model systems (Belelli et al, 1989; Bitran et al, 1991; Wieland et al, 1991).
Anticonvulsant profile (animal models/electrophysiology)
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Pharmacology
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There is ample evidence indicating a role for allopregnanolone in the treatment of seizures and status epilepticus (SE). Allopregnanolone has anticonvulsant properties
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in a variety of acute seizure models, including the pentylenetetrazol (PTZ), 6Hz, The acute anticonvulsant efficacy of
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bicuculline, and picrotoxin models.
allopregnanolone in the PTZ-induced seizure model in mice is maintained upon repeat
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dosing. Allopregnanolone produces complete suppression of generalized amygdalakindled convulsions and protection against pilocarpine- or kainate-induced limbic
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seizures and SE, with higher protective index values than clonazepam. In the rat
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kainate-induced model of SE, allopregnanolone (30 mg/kg, ip) eliminated SE whether administered at either 10 minutes or at 70 minutes following kainate administration,
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whereas diazepam (5 mg/kg, ip) was only effective at 10 minutes following kainate administration.
These results support the hypothesis that enhancement of extra-
synaptic GABAA receptor function by allopregnanolone may provide anticonvulsant
efficacy when prolonged seizure activity has become pharmaco-resistant to benzodiazepine treatment.
Mechanism(s) of action Mammalian GABAA receptors are heteropentameric chloride-conducting ion channels that mediate fast inhibition of synaptic transmission via a reduction of neuronal membrane excitability. These ionotropic receptors are called GABAA receptors to 13 Page 13 of 166
distinguish them from metabotropic GABA receptor (G-protein coupled) (GABAB) receptors that mediate a slower form of synaptic inhibition. Allosteric potentiation of GABAA receptor function by allopregnanolone has been
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extensively documented (Belelli, 2002; Belelli et al, 2005). Consistent with this literature, SAGE-547 potentiated GABA-mediated currents from recombinant human
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GABAA receptors expressed in heterologous mammalian cell lines. SAGE-547 produced a potent, concentration-dependent enhancement of GABA-evoked currents
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recorded using whole-cell patch electrophysiology from Ltk-1 cells expressing α1β2γ2
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receptors, with a half maximal effective concentration (EC50) of 60 nM and a maximal potentiation of 380% for agonist (EC20)-induced currents. SAGE-547 also produced a
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potent enhancement of α4β3δ receptors, with an EC50 of 80 nM and a maximal potentiation of 418% for agonist (EC20)-induced currents.
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In addition to allosteric enhancement of channel function, allopregnanolone
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modulates the binding of a variety of other ligands to the GABAA receptor, including the picrotoxin/convulsant site labeled by [35S]-t-butylbicyclophosphorothionate
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(TBPS) (Concas et al, 1996). Consistent with this literature, SAGE-547 potently inhibited [35S]-TBPS binding, displacing the radioligand from rat cerebral cortex membranes with an inhibition constant (Ki) of 18 nM.
Toxicology
The minimum lethal doses for allopregnanolone in mice, rats, and rabbits are 20, 15, and 7 mg/kg intravenously, respectively. Based on the correction for body surface area across the species, these are equivalent to human doses of 1.6, 2.4, and 2.25 mg/kg intravenously, or 112, 168, and 158 mg in a 70 kg human (Gyermek et al, 1968). 14 Page 14 of 166
A recently published abstract presented the determination of maximum tolerated doses (MTD) of allopregnanolone in neonatal beagle dogs after bolus and i.v. infusions (Steinmetz et al, 2013). One pup administered allopregnanolone via i.v.
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bolus (50 mg/kg), was not responsive to stimuli and exhibited, shallow rapid breathing but fully recovered without intervention. One pup administered 20 mg/kg
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allopregnanolone over a 4 hr i.v. infusion, fell asleep approximately 30 min post dose
and recovered without intervention. No allopregnanolone-related adverse effects on
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chemistry or hematology labs were observed. Of note, studies with allopregnanolone
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by the same investigators suggested that the presence of isoflurane anesthesia resulted in an MTD of 2-fold in one of the three donors. Although SAGE-547 shows the potential to induce CYP2B6, the increase was small
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at the highest concentration tested. Clinical exposures are targeted at 150 nM, which are well below the 30-50 μM required for induction of the enzyme. The potential for SAGE-547 (1 and 10 µM) to inhibit human CYP1A2, CYP2C9, CYP 2C19, CYP2D6, and CYP3A4 was investigated in vitro utilizing human liver
microsomes incubated in the presence of clinically relevant marker substrates. No inhibition was observed at 1 µM of SAGE-547. At 10 µM, no inhibition was observed for any of the CYPs, except for CYP2C9, which showed 47% inhibition. This result was followed up by determining half maximal inhibitory concentration (IC50) and Ki for CYP2C9 utilizing human liver microsomes and measuring formation of 4’hydroxy-diclofenac from diclofenac. IC50 was 0.41 µM and Ki was 0.256 µM. There 16 Page 16 of 166
was no evidence of time-dependent or metabolism-dependent inhibition based on monitoring IC50-shift after pre-incubation. SAGE-547 has the potential to alter the
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metabolism of CYP2C9 substrates when administered concomitantly.
Tolerability and adverse effect profile
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With systemic exposures up to 150 nM, no drug-related serious TEAEs have been reported. Drug related TEAEs reported with i.v. allopregnanolone are generally mild,
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the most frequently reported (>5% patients) being feelings of intoxication, sedation,
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and vertigo. One patient experienced an anxiety attack, which is potentially a withdrawal effect. Clinical observations in the i.v. studies included decreased saccadic
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eye movements, reduced episodic memory, as well as reduced plasma levels of LH and FSH. (Timby et al, 2006; Timby et al, 2011; van Broekhoven et al, 2007; Kask et
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al, 2008; Kask et al, 2009).
Efficacy data and ongoing study
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An open-label Phase I/II clinical trial was initiated to study the safety, tolerability and
efficacy of SAGE-547 in at least 10 adult patients with SRSE. This trial is enrolling patients who have been in SE for at least 24 h despite treatment with first and second line SE treatments and have either failed to have SE controlled after 24 hours on a third-line general anesthetic (GA) agent or if SE was controlled by a GA have failed at least 1 wean attempt. A patient is excluded from the trial if pregnant or lactating, or if the patient has a known allergy to progesterone or allopregnanolone, has clinically significant ECG abnormalities, has a significant medical or surgical condition that may compromise vital organ systems, has been exposed to another experimental treatment within 30 days, is receiving a continuous 17 Page 17 of 166
i.v. AED (third-line agent) for seizure suppression or burst-suppression that will require greater than 24 h to wean, has enrolled in this trial previously, or if the SRSE was due to anoxic/hypoxic encephalopathy.
The figure below demonstrates the
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design of the screening and treatment periods of this trial. Following the treatment period, there will be an acute two day follow-up period and an extended three-week
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follow-up period.
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Figure 1: Trial design of SABE-547 in Super-refractory status epilepticus (SRSE)
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The primary objective of this trial are to evaluate the safety and tolerability of SAGE-
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547 injection in SRSE patients as assessed by monitoring treatment-emergent adverse
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events (TEAE), EEG, physical and neurological examinations, vital signs, clinical laboratory measures, ECGs and concomitant medication usage.
The secondary
objective of this trial is to assess the efficacy of SAGE-547 in SRSE, a assessed by the need to place the patient back into general anesthesia for seizure control during administration of SAGE-547 prior to taper.
Other secondary objectives include
duration of response, as well as changes in behavior as measured by rating scales of agitation, depth of coma, and survival. This trial is ongoing. To date, 4 patients have completed the full 5 day administration of SAGE-547 at a target plasma exposure of 150 nM and 30-day follow-up period. All have met the key efficacy endpoint of SE control during SAGE-547 administration. To date there have been no drug-related
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serious TEAEs in these patients.
Planned studies
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larger scale controlled trial in a similar population of SRSE patients.
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Depending upon the outcome of the Phase I/II trial, the plan is to follow-up with a
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AMP-X-0079 A. Pesyan1, R. J Porter2 AurimMed Pharma, Park City, Utah, USA1
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University of Pennsylvania, Philadelphia, PA, and USUHS, Bethesda MD, USA2
Introduction and rationale for development
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AurimMed Pharma, Inc. is developing innovative prescription drugs using the Privileged Structure Platform™ (PSP) strategy to generate lead compounds. The PSP
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approach ensures that the process of drug design proceeds exclusively from a highly enriched pool of pharmaceutically and medicinally relevant chemical structures,
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greatly shortening product development times while enhancing clinical success (Muller, 2003; DeSimone et al., 2004; Costantino and Barlocco, 2006; Duarte et al.,
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2007). The PSP strategy has been used in the development of novel anti-seizure drug
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candidates with potential superior efficacy and greatly diminished adverse effects.
Pharmacology
Anticonvulsant profile (animal models/electrophysiology) Based on studies in animal models, AurimMed Pharma’s most advanced AED candidate, AMP-X-0079, has a very broad spectrum, with the potential to become a superb anti-seizure drug for a variety of seizure types, including absence/petit mal, tonic-clonic and myoclonic seizures as well as status epilepticus. In addition to the
compound’s broad spectrum of activities across a number of animal models (Tables 1 and 2), it has (in rodent models) good oral bioavailability, CNS penetration, long duration of action, good neurological safety margins (Protective Indices, PIs), and substantial potency. 20 Page 20 of 166
AMP-X-0079 anticonvulsant data included in Tables 1 and 2 were largely derived from the Anticonvulsant Screening Program of NINDS, NIH. As one can see, AMPX-0079 is active in all the models tested, including the new semi-chronic mesial
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temporal lobe epilepsy model. Protective Index (PI) = TD50/ED50. (“Toxicity” is defined here as rotarod motor impairment in mice and a battery of tests to determine
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neurological deficit as indicated by ataxia or other minimal motor impairment (MMI) in rats.)
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In studies conducted by the NIH and the US Department of Defense (DOD), AMP-X-
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0079 is active in models of chemically induced status epilepticus (SE), both when administered at the time of the chemical insult (time zero) as well as 30 minutes after
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the appearance of seizures; the compound is therefore effective in both the prevention and the treatment of SE. Moreover, in a pilocarpine-induced model of SE, followed
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by extensive, 9 day, evaluation in a Morris water maze task, AMP-X-0079 preserved
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cognition, spatial learning and memory. The compound also demonstrated substantial in vivo neuroprotective effects in the dentate gyrus, CA1, and CA3 hippocampal
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neurons in the brains of a vast majority (87%) of the treated animals (results confirmed histologically). In the pilocarpine insult and SE, 100% of the AMP-X0079-treated animals survived compared to 54% of controls. In addition, the compound is active against non-convulsive seizures in benzodiazepine-resistant electrographic status epilepticus (ESE), confirmed by EEG studies (Lehmkuhle et al.,
2009).
AMP-X-0079 has been shown in in vivo studies to be orally bioavailable, fast-acting (rapid oral absorption within 15 minutes), with a reasonably long pharmacological half-life in animal models. The compound passes the blood-brain barrier, thereby manifesting its pharmacological effects directly in the central nervous system. 21 Page 21 of 166
Because of its unique pharmacological profile and significant suppression of ESE, the lead candidate (AMP-X-0079) was tested against a nerve agent (i.e., soman) by the U.S. Army Medical Research Institute of Chemical Defense (USAMRICD) of the
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DOD. AMP-X-0079 is one of the few drugs capable of terminating ongoing status epilepticus seizures due to this nerve agent. It controls seizure very rapidly (typically
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50%, with a half-life from 2-8 h after oral administration. In vitro metabolic profiling was conducted in cryopreserved human, mouse, rat, and dog hepatocytes, and reveals essentially four discreet metabolites. Although structural identification of these metabolites has not been conducted to date,
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their molecular mass suggests that they all result from single hydroxylations. In addition, there is no evidence for the occurrence of unique human metabolites.
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Drug interactions Although no formal drug interaction studies have been conducted, in vitro CYP
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inhibition (IC50) is >30 µM for all major isozymes, suggesting low potential for SAGE-217 to inhibit the metabolism of substrates for those enzymes. Induction of
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drug metabolizing enzymes assessed in human hepatocytes indicates low level of
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induction of CYP3A4 and CYP2B6, suggesting that SAGE-217 has the potential to
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alter the pharmacokinetics of substrates for those enzymes.
Efficacy data
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Tolerability and side effect profile
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To date, no human studies have been completed with SAGE-217.
Planned studies
Currently, , to support a first in man (FIM) study, a number of IND-enabling toxicology studies are planned or on-going, including 28-day general toxicology studies in rats and dogs, a genetic toxicity battery of Ames, rat micronucleus and Comet assays, and a safety pharmacology battery of rat CNS, rat respiratory and dog telemetry studies. In addition, to support later stage clinical investigations and a potential market launch, Sage Therapeutics will perform sub-chronic (3-month) and chronic (6 or 9-month) studies in rats and dogs, reproductive toxicology studies with 110 Page 110 of 166
Seg II in rats and rabbit. Rat Seg I and Seg III, a battery of abuse liability of drug dependence, drug discrimination and self administration, and carcinogenicity studies in rats and mice are also planned. Pending outcome of these trials, a Phase III clinical
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Valnoctamide and sec-Butylpropylacetamide (SPD): Second Generation Drugs to Valproic Acid (VPA)
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M. Bialer,1 S. Kadosh2 and B.Yagen1 Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew
StatExcellence, Kfar Saba, Israel
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University of Jerusalem, Israel
CH3
CH2
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CH3
CH3
CH2
CH
*
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* CHCONH2 CH2
* CHCONH2 CH2
CH3
sec-Butyl-propylacetamide (SPD)
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Valnoctamide (VCD)
CH2
CH
*
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CH3
CH3
Introduction and rationale for development Valnoctamide (VCD) is a CNS-active chiral constitutional isomer of valpromide, the corresponding amide of valproic acid (VPA). Since EILAT XI (2012), VCD underwent phase IIb clinical trial in patients with acute mania. VCD's one-carbon homologue sec-butyl-propylacetamide (SPD) was evaluated in a wide array of anticonvulsant models (White et al., 2012; Pouliot et al., 2013; Shekh-Ahmad et al., 2013). Both VCD and SPD possess two stereogenic centers in their chemical structure (denoted above with the asterisk *) and exhibit stereoselective pharmacokinetics (PK) in humans (VCD) and animals (Bialer and Yagen, 2007; Bialer, 2012). Consequently, the pharmacodynamics (PD; anticonvulsant activity) and PK of the four individual 112 Page 112 of 166
stereoisomers of VCD and SPD were evaluated in several rodent anticonvulsant models including: maximal electroshock (MES), 6Hz psychomotor, subcutaneous metrazol (scMet) and the pilocarpine- and soman-induced status epilepticus (SE) (Hen
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et al., 2013; Shekh-Ahmad, 2014). The PK-PD (anticonvulsant activity) relationship of VCD and SPD stereoisomers were evaluated following i.p. administration (70 or 60
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mg/kg) to rats. Induction of neural tube defects (NTDs) by VCD and SPD stereoisomers was evaluated in a mouse strain highly-susceptible to teratogen-induced
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NTD.
Pharmacology
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Anticonvulsant profile (animal models/electrophysiology) Valnoctamide (VCD)
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VCD (racemate and/or its individual enantiomers) demonstrated anticonvulsant
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activity in a wide array of anticonvulsant models in mice and rats (MES, scMet and 6Hz, kindling) as described in the previous Eilat (EILAT X & XI) Conference
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manuscripts (Bialer et al., 2010 & 2013). In mice VCD four individual stereoisomers exhibited similar anticonvulsant activity
to one another as well as to racemic-VCD in the scMet and 6Hz tests, while at the MES test (2R,3R)-VCD was more potent than its enantiomer (2S,3S)-VCD and diastereoisomer (2S,3R)-VCD. In rats (p.o.) racemic-VCD and its four individual stereoisomers exhibited similar anticonvulsant activity in the MES test while (2R,3S)-VCD was the most potent compound at the scMet test with an ED50 value 5-
times more potent than the racemate (Shekh-Ahmad et al, 2014). Racemic-VCD as well as (2R,3S)-VCD and (2S,3S)-VCD administered at seizure onset blocked the pilocarpine-induced SE with similar ED50 values of about 40 113 Page 113 of 166
mg/kg. However, racemic-VCD and its individual strereoisomers lost this anti-SE activity when given (75-100 mg/kg) 30 min after seizure onset (Shekh-Ahmad et al., 2014).
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Racemic-VCD administered with the standard medical countermeasures at treatment delays of 5 min, 20 min and 40 min after seizure onset was capable of stopping
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soman-induced SE seizures with ED50 values of 26mg/kg, 60mg/kg and 62mg/kg, respectively. Following administration of VCD the average latency (sec) for
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electrographic seizure termination (mean±SEM) at 5 min, 20 min and 40 min was:
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115±15, 497±15 and 1,336±318, respectively . VCD is one of the few drugs effective
sec-Butylpropylacetamide (SPD)
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at 40 min delay at the soman-induced SE model (Shekh-Ahmad et al., 2014).
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Racemic-SPD had a wide spectrum of anticonvulsant activity similar to VPA but was
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4-30 times more potent than VPA in a wide array of anticonvulsant animal models (Shekh-Ahmad et al., 2013). Three SPD individual stereoisomers: (2R,3R)-SPD,
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(2S,3S)-SPD and (2R,3S)-SPD, exhibited anticonvulsant activity similar to racemicSPD, while (2S,3R)-SPD exhibited less potent anticonvulsant activity at the rat (po) MES model (Hen et al., 2013).
SPD stereoisomers, administered 30 min after the first observed Stage 3 motor seizure at the lithium-pilocarpine induced SE model, prevented the expression of further convulsive seizures in a dose-dependent fashion with ED50 values ranging
between 95-135 mg/kg. (2R,3R)-SPD was the least potent SPD stereoisomer (ED50 >130 mg/kg) (Hen et al., 2013). SPD and its individual stereoisomers were capable of stopping soman-induced SE seizures with ED50 values ranging between 40 to 71 mg/kg. Following administration 114 Page 114 of 166
of SPD individual stereoisomers the average latency (sec) for electrographic seizure termination at the 20-min treatment delay time (mean±SEM) was: 550±149; n=16 [(2R,3R)-SPD], 994±280; n=8 [(2R,3S)-SPD], 719±216; n=15 [(2S,3R)-SPD],
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1589±684; n=13 [(2S,3S)-SPD] . All four individual SPD stereoisomers had a steep dose response curve with Hill (shape) coefficient of 4.5-8.9 that lead to a tight 95%
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confidence interval around their ED50 values. (2R,3R)-SPD was more potent than racemic-SPD as well as SPD three other individual stereoisomers (p
